This invention relates to a method for controlling copolymer architecture by a two part process. In the first step, a monomer analysis is obtained from a test polymerization having constant rate co-monomer addition. In the second step a copolymer is polymerized using a co-monomer feed rate that has been adjusted based on the monomer analysis to produce a copolymer with highly controlled polymer architecture.
In the process of polymerizing two or more monomers to form a copolymer, it is common that the monomers may have different reaction rates. The mismatch in reaction rates can be partially corrected by using a slow-addition process in which the reactor initially contains the slower reacting monomer (M2), and the faster reacting monomer (M1) is added at a constant feed rate over some period of time. Because of the difference in reactivity of the monomers, expressed as reactivity ratios (r), the composition of the copolymer may be rich in one of the co-monomers (M1) in the initial stages of polymerization, and rich in the other co-monomer at the end of polymerization. This produces a tapered polymer architecture with a block rich in (M1), and then, as (M1) is depleted, the other monomer (M2) will, form a block rich in (M2) monomer.
Unfortunately this common polymerization method offers little control over the polymer architecture when monomers of significantly different reaction rates are co-polymerized.
Control of polymer architecture is an effective way to create several new and differentiated products. For example, a random copolymer (ideal copolymer) would be expected to have markedly different properties from a blocky copolymer of the same composition. Therefore, new products with improved performance can be developed by a deliberate change in the polymer architecture. Since it was found that many polymers have a more blocky structure, due to miss-matched polymerization rates, it is desirable to develop a method to control polymer architecture.
Surprisingly it has been found, that copolymer architecture can be controlled by a two part process. A monomer analysis is obtained from a test polymerization having constant rate co-monomer addition, and second the co-monomer feed rate is adjusted based on the monomer analysis to produce a copolymer with highly controlled polymer architecture. This method facilitates new product development, and leads to new products with improved properties, designed for a specific application.
The present invention is directed at a method for controlling the polymer architecture of a copolymer comprising the steps of:
a) conducting a test polymerization of co-monomers comprising:
1) charging the slower reacting monomer to a reactor, and beginning the polymerization;
2) delay-feeding the faster reacting monomer(s) at a constant rate over a period of time:
3) measuring periodically the residual monomer level of the slower reacting monomer;
4) calculating the percent of slow monomer used up in each time period; and
5) calculating a feed rate for the second monomer to obtain the desired polymer architecture; and
b) conducting a polymerization of said co-monomers comprising:
1) charging the slower reacting monomer to a reactor, and beginning the polymerization; and
delay-feeding the faster reacting monomer(s) at the variable rate determined in step a)4, to produce a copolymer having the desired polymer architecture.